首先，发现问题的arcanist版本如下：
arc version
arcanist d92fa96366c0ed50e4257508148aa75192d4fb1f (20 Jun 2019)
libphutil b416093386a225b1d9a2de906899b94cbf4babcb (8 Jul 2019)
错误现象为执行arc feature或arc branch时，提示：
[2019-07-20 13:30:05] ERROR 8: Undefined offset: 1 at [D:\phabricator\arcanist\src\repository\api\ArcanistGitAPI.php:1094]
arcanist(head=master, ref.master=d92fa96366c0), phutil(head=master, ref.master=b416093386a2)
#0 ArcanistGitAPI::getAllBranches() called at [<arcanist>\src\workflow\ArcanistFeatureWorkflow.php:89]
#1 ArcanistFeatureWorkflow::run() called at [<arcanist>\scripts\arcanist.php:394]
[2019-07-20 13:30:05] ERROR 8: Undefined offset: 2 at [D:\phabricator\arcanist\src\repository\api\ArcanistGitAPI.php:1094]
arcanist(head=master, ref.master=d92fa96366c0), phutil(head=master, ref.master=b416093386a2)
#0 ArcanistGitAPI::getAllBranches() called at [<arcanist>\src\workflow\ArcanistFeatureWorkflow.php:89]
#1 ArcanistFeatureWorkflow::run() called at [<arcanist>\scripts\arcanist.php:394]
[2019-07-20 13:30:05] ERROR 8: Undefined offset: 3 at [D:\phabricator\arcanist\src\repository\api\ArcanistGitAPI.php:1094]
arcanist(head=master, ref.master=d92fa96366c0), phutil(head=master, ref.master=b416093386a2)
#0 ArcanistGitAPI::getAllBranches() called at [<arcanist>\src\workflow\ArcanistFeatureWorkflow.php:89]
#1 ArcanistFeatureWorkflow::run() called at [<arcanist>\scripts\arcanist.php:394]
[2019-07-20 13:30:05] ERROR 8: Undefined offset: 4 at [D:\phabricator\arcanist\src\repository\api\ArcanistGitAPI.php:1094]
arcanist(head=master, ref.master=d92fa96366c0), phutil(head=master, ref.master=b416093386a2)
#0 ArcanistGitAPI::getAllBranches() called at [<arcanist>\src\workflow\ArcanistFeatureWorkflow.php:89]
#1 ArcanistFeatureWorkflow::run() called at [<arcanist>\scripts\arcanist.php:394]
[2019-07-20 13:30:05] ERROR 8: Undefined offset: 5 at [D:\phabricator\arcanist\src\repository\api\ArcanistGitAPI.php:1094]
arcanist(head=master, ref.master=d92fa96366c0), phutil(head=master, ref.master=b416093386a2)
#0 ArcanistGitAPI::getAllBranches() called at [<arcanist>\src\workflow\ArcanistFeatureWorkflow.php:89]
#1 ArcanistFeatureWorkflow::run() called at [<arcanist>\scripts\arcanist.php:394]
Usage Exception: No branches in this working copy.